Processing was started in Fall 2001 by Ben Fry and Casey Reas. Fry was a PhD candidate at the MIT Media Laboratory and Reas was an Associate Professor at the Interaction Design Institute Ivrea. While Fry and Reas were employees of these institutions, Processing began as a personal initiative and development took place during the night and weekends through 2003. MIT indirectly funded Processing through Fry's graduate stipend and Ivrea indirectly funded Processing through Reas's salary. Due to his research agreement with MIT, all code written by Fry during this time is copyright MIT.

In summer 2003, Ivrea funded four individuals to work on the project for a few months. This resulted in Dan Mosedale's preprocessor using Antlr and Sami Arola's contributions to the graphics engine. The code for these elements are both copyright 2003 Interaction Design Institute Ivrea.

In August 2003, Reas left the Interaction Design Institute Ivrea and in June 2004, Fry left the MIT Media Laboratory. The code and complete reference written since June 2004 are copyright Ben Fry and Casey Reas.

Portions of the code were written by other contributors and are attributed in the source code. For example, portions of the graphics engine were written by Karsten Schmidt. There are many contributions to the Exhibition and Examples on the Processing.org website and these are attributed in context.

The Reference for the Language and Environment are under a Creative Commons license which makes it possible to re-use this content for non-commercial purposes if it is credited.